PB PM said:
All those extra higher end glass elements in the 28-300mm sure haven't helped it too much. The 70-300 VR shows higher resolution figures, across the entire frame, throughout most of the zoom range (particularly beyond 200mm).
Of course the 70-300mm and 28-300mm are different classes of lenses. The 28-300mm is an all in one, for situations where flexibility is of higher value. The 28-300mm also has higher barrel and pincushion distortions. Thus correcting for that distortion additionally reduces image resolution.
Please go to kenrockwelldotcom and read why sharpness and lens resolution isn't even worth talking about.
"Any good modern lens is corrected for maximum definition at the larger stops. Using a small stop only increases depth..." Ansel Adams, June 3, 1937, in a reply to Edward Weston's request for lens suggestions, page 244 of Ansel's autobiography. Ansel was telling him to stop worrying about lens sharpness, since all the ones he was considering were sharp. This was the 1930s. Today even crappy lenses, including plastic lenses on most disposable cameras, are sharp when used properly.
any discussion on sharpness is in the end trivial and for no-one but pixel peepers who spend more time on their computers in photoshop than out making art with their cameras. sure there are crappy lenses out there that have the sharpness of a rusty pair of safety scissors, but if a lens is sharp... it's sharp. Anything different between two sharp lenses is nothing anyone is ever going to see on a print. So... besides that... what's better about the 70-300? Cause I'm still not seeing anything why one would recommend it unless the recommendee could not afford better. (and btw, most modern cameras, including the d700 mentioned by OP correct automatically or lens distortions w/o losing any visible resolution. So once again, trivial point.)